Effect of Process Parameters on Crystal Types and Microstructure of TiO2 Nanocrystalline Powders

TiO2 nanocrystalline powders were prepared by sol-gel method with different process parameters. The phase, morphology and the luminescent property of TiO2 nanocrystalline powders were characterized by XRD, SEM and PL, respectively. The results indicated that the synthesized TiO2 nanocrystalline powders were transformed from anatase into rutile with the increasing of heat treatment temperature, which begin at the temperature of 500 oC and was almost completed at the temperature of 700 oC. And with the increasing of pH value the rutile proportion become larger, the nanograins become fine and powders agglomeration was decreased. The good performance TiO2 nanocrystalline powders were obtained when prepared temperature was 500°Cand pH value was 4. PL results show broad and strong luminescence band appeared near 470nm when TiO2 nanocrystalline powders were excited at 325nm at room temperature.

Synthesis and Optical Properties Study of ZnS Crystallitic Films

This manuscript presents the synthesis and characterization of ZnS crystallitic films on ITO conducting glass by a simple hydrothermal method, based on sulfuration conversion from Zn nanocrystallines which are synthesized by pulse-plating technology. X-ray diffraction (XRD), scanning electron microscopy (SEM) and equipped with Oxford 7538 (EDS) analyzer techniques were used to characterize the Zn nanocrystallines and the novel ZnS crystallitic films. The results showed that ZnS crystallitic films were wurtzite, uniform and compact. Furthermore, the existence of Zn nanocrystallines and the complexing agent 5-sulfosalicylate influenced the microsopic morphology of ZnS crystallitic films. The optical properties, band gap energy and the size of nanocrystals were studied by UV-vis spectrophotometer measurements. A photoluminescence (PL) study of the ZnS at room temperature (300 K) indicates a strong luminescence band at energy 5.3 eV.

Defect Studies of GaN under Large Hydrostatic Pressure

ABSTRACTGaN plays a key role in the exploration of the properties of group-Ill nitrides. As grown GaN often shows a high electron concentration, e.g. 1019 cm−3, of as yet unidentified origin. Applying large hydrostatic pressure we studied the behavior of these donors and a frequently observed strong luminescence band at 3.42 eV. We find a drop of the electron concentration to 3×1017 cm−3 at 27 GPa and derive a binding energy of 126 meV for the neutral singlet donor level at this pressure. Such a pressure behavior of a donor is consistent with the model of strongly localized defects. Within the framework of a bandstructure calculation we predict the neutral level of this donor at 0.40 ± 0.10 eV above the conduction band edge at ambient pressure.